The proposed research involves studies of cell membrane receptors for prolactin, growth hormone and insulin. The research is designed to illuminate the dynamic state of receptors in target tissues and to clarify the importance of receptors in hormone action. As an initial phase of this research, receptors for prolactin, growth hormone and insulin are to be purified and characterized. Antibodies to purified receptors will be generated and used in studies of the biosynthesis and turnover of receptors. They will also be employed for the development of radioimmunoassays of receptors. The latter, in turn, will be utilized to clarify the relationship between specific binding and immunochemical receptor sites. Radioreceptor assays for lactogens and growth hormone have been used to identify and measure several "new" placental lactogens. We propose to continue these studies by purifying and chemically characterizing these hormones. Several, particularly sheep, cow and goat placental lactogen, have effects very similar to human growth hormone (hGH) because like hGH, they have both potent growth hormone and prolactin like activity. No other growth hormones share this property. Hence it may be that structurally sheep placental lactogen and hGH are very similar and it is conceivable that one of the placental lactogens might be a clinically useful growth promoting agent in GH deficient dwarfs. By examining the biological role of placental lactogens in various species one may gain important new insight into the function of this interesting hormone of pregnancy.